<template>
  <div class="pagination">
    <button @click="changePageNum(pageNo-1)" :disabled="pageNo===1">上一页</button>
    <button v-show="startAndEnd.start>1" @click="changePageNum(1)">1</button>
    <span v-show="startAndEnd.start >2">...</span>
    <button :class="{active:pageNo===startAndEnd.start + index}" v-for="(_,index) in (startAndEnd.end-startAndEnd.start + 1)" :key="_" @click="changePageNum(startAndEnd.start + index)">{{startAndEnd.start + index}}</button>
    <button v-show="startAndEnd.end < totalPage -1">···</button>
    <button v-show="startAndEnd.end < totalPage" @click="changePageNum(totalPage)">{{totalPage}}</button>
    <button @click="changePageNum(pageNo+1)" :disabled="pageNo===totalPage">下一页</button>

    <span>共 {{total}} 条</span>
  </div>
</template>

<script>
export default {
    name:'Pagination',
    data() {
        return {};
    },
    props: ['total', 'pageNo', 'pageSize', 'continues'],
    computed: {
        // 计算总页码
        totalPage() {
            const { total,pageSize } = this;
            return Math.ceil(total / pageSize);
        },
        // 计算开始和结束页码
        startAndEnd() {
            const { continues,pageSize,pageNo,totalPage } = this;
            let start,end;
            if(continues > totalPage) {
                start = 1; // 起始页
                end = totalPage; // 结束页
            }else {
                start = pageNo - parseInt(continues / 2);
                end = pageNo + parseInt(continues / 2);
                // 起始页小于1时
                if(start < 1){
                    start = 1 // 起始页不能小于1 只能从1开始
                    end = continues
                }
                // 结束页超出了总页码时
                if(end > totalPage) {
                    end = totalPage
                    start = totalPage - continues + 1
                }
            }
            return {start,end};
        }
    },
    methods: {
        // 单击按钮 实现分页
        changePageNum(pageNum){
            this.$emit('get-pageNo',pageNum)
        }
    }
}
</script>

<style lang="less" scoped>
.pagination {
  text-align: center;
  button {
    margin: 0 5px;
    background-color: #f4f4f5;
    color: #606266;
    outline: none;
    border-radius: 2px;
    padding: 0 4px;
    vertical-align: top;
    display: inline-block;
    font-size: 13px;
    min-width: 35.5px;
    height: 28px;
    line-height: 28px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    border: 0;

    &[disabled] {
      color: #c0c4cc;
      cursor: not-allowed;
    }

    &.active {
      cursor: not-allowed;
      background-color: #c81623;
      color: #fff;
    }
  }
  span {
    display: inline-block;
    line-height: 28px;
    font-size: 14px;
    color: gray;
    vertical-align: middle;
  }
}
</style>